Along with the development of communication technology, various antenna modules have been invented. The phase array module in the antenna module includes a plurality of phase shifters. The frequencies applicable to 5G communication are, for example, 28 GHz and 39 GHz. The phase shifter must be wide enough to allow the antenna module to be applied to both frequencies simultaneously.
To achieve a wide frequency band, it is necessary to maintain low RMS phase error and low RMS gain error throughout the frequency band. The RMS phase error is the average of the phase error of the phase shifter. The RMS gain error is the average of the insertion loss variation of the phase shifter. For example, the RMS phase error may be calculated according to the following equation (1), and the RMS gain error may be calculated according to the following equation (2).
RMS phase error=
                              RMS          ⁢                                          ⁢          phase          ⁢                                          ⁢          error                =                                            1                              N                -                1                                      ⁢                                          ∑                                  i                  =                  2                                N                            ⁢                                                                                      θ                                          Δ                      ⁢                                                                                          ⁢                      i                                                                                        2                                                                        (        1        )            RMS gain error=
                              RMS          ⁢                                          ⁢          gain          ⁢                                          ⁢          error                =                                            1                              N                -                1                                      ⁢                                          ∑                                  i                  =                  2                                N                            ⁢                                                                                                            A                      i                                        -                                          A                      Avg                                                                                        2                                                                        (        2        )            
N is the number of states, i is the i-th state, θΔi is the error between the i-th state and the ideal state, Ai is the insertion loss of the i-th state, and AAvg is the average of the insertion loss of all states.
A traditional 5 bits switching type phase shifter includes 5 phase shifting units with different angles. Through the switching of the ON state/OFF state of each phase shifting unit, 32 different phase states can be formed.
However, in the traditional phase shifter, it is quite difficult to maintain a low enough RMS phase error and a low enough RMS gain error throughout the frequency band.
Therefore, how to design a phase shifter that can be applied to broadband has become the main research direction of future development.